A fuel cell power generation system is mainly composed of a fuel reforming device and a fuel cell body, and has attracted attention as a dispersed type power source for households, etc. The fuel reforming device converts a fuel gas, such as city gas, into a hydrogen-rich reformed gas, and supplies it to the fuel cell body. The fuel cell body reacts the reformed gas with air electrochemically to generate electrical power.
In such a fuel cell power generation system, if operation is stopped instantaneously, a combustible gas, such as hydrogen or methane, moisture, and so on remains in different parts of the fuel reforming device or the like. During maintenance and inspection, the combustible gas may leak to the outside, or moisture may form dew on a catalyst, deteriorating the catalyst.
Thus, Japanese Patent Application Laid-Open No. 2001-277137, for example, proposes to feed air into the fuel reforming device at the time of stopping power generation to fill the fuel reforming device with air, thereby removing residual matter, such as a combustible gas or moisture, from the interior of the fuel reforming device. However, oxygen in the air is likely to deteriorate the catalyst of the fuel reforming device (especially, a Cu/Zn-based LTS catalyst used in a CO conversion reaction).
Hence, Japanese Patent Application Laid-Open No. 2001-180908, for example, proposes that a precious metal catalyst minimally deteriorated by oxygen be applied to the fuel reforming device. However, the precious metal catalyst is lower in catalytic efficiency than the Cu/Zn-based catalyst (about 1/5 to 1/10 expressed as volume ratio), thus resulting in the upsizing of the fuel reforming device, and posing difficulty in heating the entire device uniformly.
In the light of these disadvantages, Japanese Patent Application Laid-Open No. 2000-277137, for example, proposes performing a combustion reaction between a fuel gas or a reformed gas and air to produce an inert gas mainly consisting of nitrogen and carbon dioxide; storing the inert gas in a tank for a while; and withdrawing the inert gas from the tank when stopping operation to fill the inert gas into the fuel reforming device, thereby removing residual matter, such as a combustible gas or moisture, from within the fuel reforming device.
Moreover, Japanese Patent Application Laid-Open No. 2000-277138, for example, shows a system newly provided with a second fuel cell body different from the fuel cell body for power generation, and proposes performing an electrochemical reaction between a reformed gas and air, or air discharged from the fuel cell body for power generation, in the second fuel cell body to discharge low-oxygen, nitrogen-rich exhaust air from the second fuel cell body, so as to utilize it as an inert gas; and, when stopping operation, filling the inert gas into the fuel reforming device, thereby removing residual matter, such as a combustible gas or moisture, from within the fuel reforming device.
With the aforementioned means proposed in the above-described Japanese Patent Application Laid-Open No. 2000-277137, however, unless the fuel gas or reformed gas and air are subjected to the combustion reaction stoichiometrically equally, oxygen or the combustible gas remains in the inert gas. This makes it actually difficult to produce the inert gas. Also, the tank for storage of the inert gas has to be rendered ready for use, causing the upsizing and cost increase of the system.
These are marked disadvantages to the utilization of the system as a dispersed type power source for households.
With the aforementioned means proposed in the above-described Japanese Patent Application Laid-Open No. 2000-277138, on the other hand, air discharged as a result of the electrochemical reaction between the reformed gas and air, or air discharged from the fuel cell body for power generation, performed in the second fuel cell body is utilized as the inert gas. Thus, oxygen is not entirely consumed in the second fuel cell body, but remains in the inert gas. This makes it actually difficult to produce a complete inert gas. Also, the fuel cell body for production of the inert gas has to be rendered ready for use, thereby causing the upsizing and cost increase of the system. These are marked disadvantages to the utilization of the system as a dispersed type power source for households.
Under these circumstances, it is the object of the present invention to provide a technology which can reliably remove residual matter, such as a combustible gas or moisture, and oxygen, without leaving them within a fuel reforming device of a fuel cell power generation system, at a low cost and with a compact configuration.